1. Field of the Invention
The present invention relates to a protective encapsulation for a phototransducer.
2. Description of Related Art
Phototransducers are employed in a wide array of applications. Herein, xe2x80x9cphototransducerxe2x80x9d includes both receiver devices (e.g., photosensitive diodes) which produce an electrical output in response to sensed light as well as transmitter devices (e.g., light emitting diodes) which produce light in response to an electrical input. Herein, xe2x80x9clightxe2x80x9d includes not only visible light, but also ultraviolet and infrared radiation.
A photoelectric sensor is an example of a device that typically uses one or more phototransducers. Herein, xe2x80x9cphotoelectric sensorxe2x80x9d refers to an industrial control sensor device that comprises at least one receiver-type phototransducer, and typically also a transmitter-type phototransducer (though often not in the same package). In an industrial control sensor device of this type, light is used as a transducer mechanism, but the sensed parameter is usually considered to be some other parameter, for example, the presence of an object within the field of view of the photoelectric sensor (presence sensor) or the distance of an object from the photoelectric sensor (proximity sensor). Different types of photoelectric sensors can operate according to different modes of operation, including transmitted beam sensing modes, retroreflective sensing modes and diffuse sensing modes. For example, in a retroreflective presence sensing mode, the transmitter emits a light beam which is received by the receiver if an object is present to reflect the light beam. When no object is present, the light beam is not reflected and therefore is not received by the receiver. Whether the receiver receives a reflected light beam thus provides an indication whether an object is present. The signal that is thereby generated may then be used for further process control.
Phototransducers are typically wafer fabricated and subsequently mounted on a substrate having first and second electrical traces for connection to the phototransducer. According to this process, one side of the phototransducer is attached to the substrate via a solder pad which is electrically connected to one of the traces, and the opposite side of the phototransducer is electrically connected to the other trace by way of a thin wire bond. A transparent encapsulant (commonly referred to as potting material) is then used to construct a dome-shaped structure that encapsulates and protects the phototransducer and the thin wire bond from pick and place machine handling, shipping shock or vibration, corrosive environments, electrical contract with other conductive elements, and so on.
It is often desirable to have more control over the shape of the dome that is constructed than is otherwise possible through conventional encapsulation techniques. Constraints may be placed on the shape of the dome based on the dimensions of the phototransducer, the dimensions of the wire bond, and/or the dimensions of the structure into which the phototransducer is ultimately incorporated. Because the encapsulant naturally tends to flow into a thin film, particular difficulty is encountered when the dome must be above a certain height in order to adequately encapsulate the phototransducer and the thin wire bond. An improved encapsulation technique for phototransducers is therefore needed.
According to a first aspect, a preferred embodiment of the invention provides a method of encapsulating a phototransducer comprising mounting the phototransducer on a substrate, depositing a surfactant on the substrate, and depositing an encapsulant on the substrate over the surfactant. The surfactant alters a surface tension of the substrate. The encapsulant forms a protective structure that protects the phototransducer.
According to a second preferred aspect, another preferred embodiment of the invention provides an apparatus comprising a substrate, a phototransducer, and an encapsulant deposit. The substrate has a surface that includes a surfactant film. The phototransducer is mounted on the substrate. The encapsulant deposit that is located on the surfactant film and encapsulates and protects the phototransducer.
According to a third preferred aspect, another preferred embodiment of the invention provides a method of encapsulating a phototransducer that is mounted on a substrate. The method consists essentially of depositing a surfactant on the substrates adjacent the phototransducer, permitting the surfactant to dry, depositing a single generally dome-shaped layer of encapsulant on the phototransducer, and permitting the encapsulant to cure on the substrate.
Other objects, features, and advantages of the present invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not limitation. Many modifications and changes within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.